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Hannibal

Video transmission - I need a primer on frequencies

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I've been trying to figure this out for some time, to no avail. I'm looking for a primer on the pros and cons of higher vs. lower frequencies (900MHz, 1.2GHz, 1.3GHz, 2.4GHz, 5.8GHz) for video transmission, while not considering the issue of environmental interference (e.g. wi-fi, phones, etc.). That's not to say that I'm not interested in interference, but I'm not interested in a discussion of which frequencies have the most gear using that frequency. What I would be interested in knowing is if there is something INHERENT in a particular frequency that makes it either more susceptible or less susceptible to interference.

Here's what I've gleaned so far. Given a particular power output, the higher frequencies have a smaller range than the lower frequencies. I hope that's right because it's the only fact that I actually have confidence in.

Now I've read numerous sources that have said lower frequencies also bypass obstructions (e.g. walls/doors) better at a given power output. But then when I think about listening to the radio, I know that when I pass through a tunnel, the FM (higher frequency) signals continue to work in the tunnel while the AM frequencies don't work. That implies to me that higher frequencies bypass obstructions better. On this issue is where I have the most confusion.

Then there's the issue of video quality with higher vs lower frequencies. I've read numerous sources that say there is no significant difference. But I've always thought that higher frequencies would tend to maintain better video quality. I would also be interested in knowing if there is something inherent in the higher or lower frequencies that makes them more susceptible to interference, ignoring the issue of which frequencies happen to be used by the public more.

So, based on what I've read on the internet so far, if lower frequencies have better range and no other significant differences, then it seems there would be no need to ever go to the higher frequencies. Somehow, I think there's more to it than that. I would also be interested to know if there are particular frequencies that are best to avoid due to possible manufacturing difficulties (i.e. there is nothing inherent in the frequency itself, but the gear being produced just happens to suck).

I'm looking more for generalizations than comparing manufacturers and particular transmitters. Any clarification would be helpful.

Thanks

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What I would be interested in knowing is if there is something INHERENT in a particular frequency that makes it either more susceptible or less susceptible to interference.

Overall, this is a location specific issue and depends on the other RF sources that may be in the local environment. For example, some of us have given up on 2.4GHz wireless video because of adverse competition from Wi-Fi sources, where as others have moved to it because of interference on their 900-1.3Ghz system. It is a unpredictable moving target, so quite frustrating. I understand you are not interested in this aspect of interference, but it is a performance issue that has affected many of us that are into wireless video. So ignoring it would be unrealistic.

Multipathing will indeed increase as frequency is increased. It is somewhat linear in behavior, so doubling the frequency can often double the multipathing hits. This can be mitigated somewhat with proper antenna choices and optimized setups. As with everything else, there is no way to know in advance if moving to a higher frequency will invite enough to ruin your day.

Here's what I've gleaned so far. Given a particular power output, the higher frequencies have a smaller range than the lower frequencies. I hope that's right because it's the only fact that I actually have confidence in.

Confidence in that statement would be found if all the RF designs played by the same rules. However, higher frequencies can involve more modern designs, so sometimes the advantages of the lower frequency's reduced path loss are compensated by the technology used in the higher frequency RF system. In the end, I've found that with quality systems, the operating frequency can often be ignored when it comes to such generalized statements.

Then there's the issue of video quality with higher vs lower frequencies. I've read numerous sources that say there is no significant difference. But I've always thought that higher frequencies would tend to maintain better video quality.

All of the popular wireless video systems I've measured have less than 5MHz bandwidth, with some as low as 3.5MHz. The bandwidth is what determines maximum possible visual resolution. The bandwidth specs vary with the different wireless video products and is rarely advertised (if you want to know it, you have to measure it). Overall, the bandwidth cannot be predicted by the frequency band being used. An exception to this is 433Mhz video designs, which are old-school AM and band limited to ≤4MHz as a courtesy to other Ham ATV hobbyists.

I'm looking more for generalizations than comparing manufacturers and particular transmitters. Any clarification would be helpful.

We have a lot of generalizations we could propose, but the bottom line is that there is no silver bullet when it comes to the perfect wireless video frequency. For everyone that claims their X-Mhz system is ideal, someone else will report that they couldn't use it in their area. So, the best choice is the one that works for YOU.

Overall, the frequency discussion has been beat to death. So, if you search around the various FPV forums you should find endless discussions regarding the best frequency for wireless video. Be prepared for a variety of opinions. :)

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I understand you are not interested in this aspect of interference, but it is a performance issue that has affected many of us that are into wireless video. So ignoring it would be unrealistic.

Of course I'm interested, but I didn't want this thread to revolve around a concept that's relatively easy to understand and is discussed in every thread I've ever read on the topic. Just trying to steer the discussion toward issues I don't understand. Obviously, it's one of the most important issues.

Multipathing will indeed increase as frequency is increased. It is somewhat linear in behavior, so doubling the frequency can often double the multipathing hits. This can be mitigated somewhat with proper antenna choices and optimized setups. As with everything else, there is no way to know in advance if moving to a higher frequency will invite enough to ruin your day.

Very helpful. Thank you.

Confidence in that statement would be found if all the RF designs played by the same rules. However, higher frequencies can involve more modern designs, so sometimes the advantages of the lower frequency's reduced path loss are compensated by the technology used in the higher frequency RF system. In the end, I've found that with quality systems, the operating frequency can often be ignored when it comes to such generalized statements.

What about 1.3 GHz? I don't remember seeing much gear using that frequency even a few years ago. So, I would presume that it's relatively new compared to 900 MHz, 1.2 GHz, and 2.4 GHz. It's also a relatively low frequency, so less multipathing, as you mentioned earlier.

All of the popular wireless video systems I've measured have less than 5MHz bandwidth, with some as low as 3.5MHz. The bandwidth is what determines maximum possible visual resolution. The bandwidth specs vary with the different wireless video products and is rarely advertised (if you want to know it, you have to measure it). Overall, the bandwidth cannot be predicted by the frequency band being used. An exception to this is 433Mhz video designs, which are old-school AM and band limited to ≤4MHz as a courtesy to other Ham ATV hobbyists.

Very helpful.

Overall, the frequency discussion has been beat to death. So, if you search around the various FPV forums you should find endless discussions regarding the best frequency for wireless video. Be prepared for a variety of opinions. :)

It's been beat to death, but not really in a scientific way for the most part (this forum being the exception of course). Believe me, my lack of knowledge is not from a lack of reading. It may have to do with too much noise from the unwashed masses drowning out the few who know what they're talking about.

I realize that different gear, different locations, and different uses will yield different results, but I need something to go on in selecting my first gear. If we assume that everything else is equal, then it seems that the lower frequencies win out on the science alone. Among the lower frequencies, it seems that 1.3 GHz is probably the least used (correct?), so I think that's where I'll start and go from there.

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What about 1.3 GHz? I don't remember seeing much gear using that frequency even a few years ago. So, I would presume that it's relatively new compared to 900 MHz, 1.2 GHz, and 2.4 GHz. It's also a relatively low frequency, so less multipathing, as you mentioned earlier.

The 1.2GHz and 1.3GHz video systems are essentially the same hardware as the 900Mhz systems. No new technology was introduced in their designs. If you are looking for practical hard data, then you can assume that a modern high quality 2.4GHz video system may have up to +6dB more effective sensitivity than what we see with the 900-1300MHz systems. So, the path loss issue due to frequency can be a don't-care thing. But 2.4GHz is a crowded RF band and as a video link solution it is no longer the Holy Grail it was a few years ago.

I realize that different gear, different locations, and different uses will yield different results, but I need something to go on in selecting my first gear. If we assume that everything else is equal, then it seems that the lower frequencies win out on the science alone.

But EVERYTHING else will not be equal. Which is why there is conflicting information in the endless opinions (think of the data as being a blend of fact and practice).

but I need something to go on in selecting my first gear.

Which leads to a more useful criteria. The biggest technical difference in the systems is in the actual manufacturer. So, if you are concerned about what is best, start with a reliable brand first then work your way down your bucket list.

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The 1.2GHz and 1.3GHz video systems are essentially the same hardware as the 900Mhz systems. No new technology was introduced in their designs. If you are looking for practical hard data, then you can assume that a modern high quality 2.4GHz video system may have up to +6dB more effective sensitivity than what we see with the 900-1300MHz systems. So, the path loss issue due to frequency can be a don't-care thing. But 2.4GHz is a crowded RF band and as a video link solution it is no longer the Holy Grail it was a few years ago.

I understand.

But EVERYTHING else will not be equal. Which is why there is conflicting information in the endless opinions (think of the data as being a blend of fact and practice).

Which leads to a more useful criteria. The biggest technical difference in the systems is in the actual manufacturer. So, if you are concerned about what is best, start with a reliable brand first then work your way down your bucket list.

Which frequency would you recommend for a newbie at this time, assuming I buy from a reputable manufacturer? Basically, here's the situation as I'm seeing it.

900 MHz to 1.3 GHz

Pros:

- theoretical advantage based on the frequency alone

- 1.3 GHz may be less crowded than the 900 MHz and 1.2 GHz

Cons:

- outdated hardware may negate any theoretical advantage

2.4 GHz

Pros:

- better, newer hardware than the lower frequencies

Cons:

- frequency is overused to the point of being ridiculous

5.8 GHz

Pros:

- better, newer hardware than 2.4 GHz?

- less used at this time than 2.4 GHz

Cons:

- theoretical disadvantage based on the frequency alone

Anyway, I'm seeing now that there probably is no best choice. I guess I'll take a harder look at individual recommendations.

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Anyway, I'm seeing now that there probably is no best choice

The local RF environment tends to make/force the choice for you. Personally, I like 900 Mhz because of the wide variety of antennas that are available and good track record of the popular manufacturers (Racewood/Lawmate). This RF band is ham legal in the USA (910 MHz) but other countries may forbid it.

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